style: apply prettier across the tree

One-shot prettier pass so the new format:check gate starts from a clean
baseline. Formatting only — no behaviour change. Generator-owned and
vendored artifacts stay untouched via .prettierignore.

src/app/onboarding/[step]/page.tsx

@@ -56,7 +56,10 @@ export default async function OnboardingStepPage({ params }: PageProps) {
   const { step: stepParam } = await params;
   const parsedStep = Number.parseInt(stepParam, 10);
 
-  if (!Number.isFinite(parsedStep) || !VALID_STEPS.includes(parsedStep as Step)) {
+  if (
+    !Number.isFinite(parsedStep) ||
+    !VALID_STEPS.includes(parsedStep as Step)
+  ) {
     notFound();
   }
   const requested = parsedStep as Step;

src/app/onboarding/layout.tsx

@@ -10,6 +10,10 @@ import type { ReactNode } from "react";
  * Content agent that follows W14b-Foundation will swap the root page's
  * redirect target once every step has real content.
  */
-export default function OnboardingLayout({ children }: { children: ReactNode }) {
+export default function OnboardingLayout({
+  children,
+}: {
+  children: ReactNode;
+}) {
   return <div className="bg-background min-h-[100svh] w-full">{children}</div>;
 }